Histology of the aortic media in dissecting aneurysms

Sections of the ascending aorta of 27 cases of dissecting aneurysm were compared histologically with the ascending aortae of 27 age- and sex-matched normotensive controls and 27 age- and sex-matched hypertensive controls. Elastic fragmentation and loss was seen to a similar degree in each series. Strip-like areas of muscle necrosis appeared to be associated as much with hypertension as with dissection. Two cases of dissecting aneurysm showed giant-cell aortitis. Mucopolysaccharide `cysts' were seen more frequently, but by no means invariably, in the dissecting series. The only abnormality that distinguished the dissecting aortae from the normotensive and hypertensive controls with any constancy was an increase in the degree of metachromasia of the ground substance.